Eating food contaminated with bugs leads to more than half a billion cases of illness a year, the World Health Organization warns. It says this “global threat” contributed to 351,000 deaths in 2010. Unsafe foods, for example undercooked meat, can cause 200 problems – from diarrhoea to cancer.

But changes in food production mean there are more opportunities for meals to harbour harmful bugs or chemicals, experts say. Unsafe foodstuffs can contain many types of harmful bacteria, viruses, parasites or chemicals. Examples include undercooked meat, fruits and vegetables contaminated with faeces and shellfish containing marine toxins.

But the WHO says investigating these outbreaks has become increasingly challenging as single plates of food often have ingredients from many countries. In its first WHO report on this issue, its director-general Dr Margaret Chan warns: “A local food problem can quickly turn into an international emergency. “Food production has been industrialised, and its trade and distribution have been globalised.

“These changes introduce multiple opportunities for food to become contaminated with harmful bacteria, viruses, parasites or chemicals.” The analysis, which pulls together scientific literature from across the globe, shows: Experts say illnesses caused by food also carry major economic risks.